Cardiac hypertrophy leading to congestive heart failure has multiple etiologies, including an a1-adrenergic receptor (a1-AR)-dependent mechanism. Rat cardiac myocytes in culture hypertrophy in response to elevated levels of catecholamines via a1-ARs that activate transcription of the fetal contractile protein genes encoding the b-myosin heavy chain (MyHC) and the skeletal muscle a-actin isoforms. Activation of these fetal genes depends on the presence of cis-regulatory M-CAT elements, binding sites for the transcription factor TEF-1. However, not all M-CAT elements in cardiac genes are responsive to a1-AR stimulation, so they must somehow differ in their interaction with TEF-1. This system provides an in vitro model to study transcription regulation during cardiac hypertrophy in vivo. In this proposal, a TEF-1 related gene (RTEF-1) is identified that is also expressed in the heart, together with TEF-1. Both TEF-1 and RTEF-1 can bind to M-CAT elements in vitro. However, whether TEF-1 or RTEF-1 specifically interacts with the a1-AR-responsive M-CAT elements in the fetal cardiac genes in vivo is not known. The following specific aims will address the hypothesis that RTEF-1 participates in catecholamine-induced cardiac hypertrophy and activation of the fetal program: Aim 1 will characterize human RTEF-1 in terms of its sequence and tissue distribution. Aim 2 will determine whether TEF-1 or RTEF-1 is responsible for the induction of the fetal program in cultured rat cardiac myocytes in response to catecholamine stimulation by co-transfection of a1-responsive promoters with expression vectors for either TEF-1 or RTEF-1. Aim 3 will characterize the ability of RTEF-1 to interact with different M-CAT elements and to be modified by phosphorylation in vitro and in vivo. Aim 4 will determine how RTEF-1 expression is regulated in cardiac myocytes during development and in culture in response to chronic catecholamine exposure and other hypertrophic stimuli.